Electric components such as relays, various switches, connectors, motors, and hard disk drives are widely used in various products.
In these electric components, pressure-sensitive adhesive sheets are attached for various purposes such as temporal tacking of parts during assembly and indication of the contents.
Such a pressure-sensitive adhesive sheet is generally constituted from a pressure-sensitive adhesive sheet base and a pressure-sensitive adhesive layer, and it is being kept in a state adhering to a release sheet until it is attached to an electric component for use.
On a surface of the release sheet (i.e., on the surface to be attached to the pressure-sensitive adhesive layer), a release agent layer is provided for improving releasability. Conventionally, a silicone resin has been used as a constituent material of the release agent layer (see, for example, JP-A 6-336574).
However, it is known that when such a release sheet is attached to a pressure-sensitive adhesive sheet, a silicone compound such as a low-molecular weight silicone resin, siloxane, a silicone oil, or the like contained in the release sheet (release agent layer) is transferred to the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet. Further, normally, the release sheet is wound up in a rolled form after the production thereof. At that time, in this state, the back surface of the release sheet is in contact with the release agent layer thereof so that the silicone compound contained in the release agent layer is transferred to the back surface of the release sheet. In this regard, it is also known that the silicone compound transferred to the back surface of the release sheet is re-transferred to the surface of a pressure-sensitive adhesive sheet when a pressure-sensitive adhesive article (which is composed of a pressure-sensitive adhesive sheet and a release sheet attached thereto) is wound up in a rolled form in manufacturing the pressure-sensitive adhesive article. Therefore, in a case where the pressure-sensitive adhesive sheet, to which such a release sheet has adhered, is attached to an electric component, the silicone compound transferred to the pressure-sensitive adhesive layer or the surface of the pressure-sensitive adhesive sheet gradually vaporizes. In this regard, it is known that the vaporized silicone compound is deposited on, for example, a surface of an electric contact portion of the electric component due to electric arc or the like generated near the electric contact portion so that a minute silicone compound layer is formed thereon.
If such a silicone compound is deposited on a surface of an electric contact portion, there is a case where electric conductivity becomes poor.
Particularly, in a case where such a pressure-sensitive adhesive sheet is attached to a hard disk drive, the silicone compound transferred to a pressure-sensitive adhesive layer or a surface of the pressure-sensitive adhesive sheet gradually vaporizes and is then deposited on a magnetic head, a disk surface, or the like. Further, there is a possibility that deposition of such a minute silicone compound gives rise to adverse effects on reading and writing of data from and to a disk of the hard disk drive.
In order to solve the above problems, attempts to develop a non-silicone-based release agent containing no silicone compound have been made (see, for example, JP-A 2005-350650).
However, a release sheet using such a non-silicone-based release agent has poor releasability, and therefore does not have sufficiently property as the release sheet. Further, there is a case where the following problems occur in such a release sheet. The problems include blocking and wrinkle occurring when the release sheet is wound up in a rolled form.